The water injection
huff and puff (WIHP) technology is regarded
as one of the important means to improve the recovery factor (RF)
of tight volcanic oil reservoirs (TVORs), but the influence of water
injection pressure (WIP) and water injection method (WIM) on the oil
recovery effect of WIHP has been rarely reported. In this paper, we
first collected the real full-diameter cores from a TVOR and then
simulated the distribution characteristics of fractures and matrix
pores after hydraulic fracturing of the reservoir through the combination
and cutting of the cores. Finally, we used the large-sized physical
simulation device for tight oil WIHP that can bear high temperature
and high pressure and a nuclear magnetic resonance instrument to conduct
experiments of five cycles of constant pressure WIHP (CWIHP) with
WIPs of 25, 32.5, and 40 MPa and step-by-step pressure rising WIHP
(SWIHP) (the WIP was 25, 30, 33, 37, and 40 MPa in order) and obtained
the liquid production law and mechanism of tight volcanic rock (TVR)
under CWIHP and SWIHP. The result shows that under the CWIHP mode,
the RF of TVR has a good power-law-positive correlation with the WIP.
However, with the increase of WIHP cycles, the RF of CWIHP always
decreases rapidly. In the WIHP of TVR, the injected water mainly collects
oil in large pores (the pore radius is greater than 0.1 μm),
and the closer the area to the outlet end of oil production and the
higher the fracture density, the higher the RF. SWIHP can also effectively
improve the RF of TVR, but compared with CWIHP with a WIP of 40 MPa,
the amount of recovered oil decreases relatively slowly with the increase
of WIHP cycles. In the first two cycles of the five cycles of WIHP,
the RF of CWIHP was higher, but from the third cycle, the RF of SWIHP
begins to be greater, and the more the number of cycles of WIHP, the
more obvious the advantage of SWIHP. When the number of WIHP cycles
exceeds 5, the oil recovery effect and the economy of SWIHP are better.
This study can provide a solid theoretical basis for the efficient
development of WIHP in TVORs.